The penetration capabilities of Flash X-ray equipment increase with voltage, particularly for heavy materials such as steel. When protection of the pulse generator or other factors require the use of a remote tubehead, the tube voltage has in the past been limited by the maximum voltage capability of available flexible interconnecting cable. Presently, high voltage flexible cables have characteristic impedances of 60 ohms or less, and should be operated at no more than about 400 kilovolts for reasonable useful cable life.
The desired higher tube voltages at the remote tubehead may be obtained by incorporating a voltage transformer into the tubehead. Previous implementations have used iron core or Tesla-type transformers which substantially increase the size and weight of the tubehead or seriously degrade the pulse waveform characteristics and energy efficiency. Transmission line transformers require an electrical transit time of at least twice the voltage pulse half amplitude width in order to achieve adequate efficiency. This would typically require a transmission line length of over 60 feet for Flash X-ray applications of a transmission line transformer using conventional coaxial cable construction.